U.S. patent application number 13/809864 was filed with the patent office on 2013-05-16 for optical film having improved optical performance, and backlight unit comprising the same.
This patent application is currently assigned to LG CHEM., LTD. The applicant listed for this patent is Sang-Choll Han, Byung-Mook Kim, Jin-Hyun Kim, Yune-Hyoun Kim, Byung-Su Park, Kwang-Seung Park. Invention is credited to Sang-Choll Han, Byung-Mook Kim, Jin-Hyun Kim, Yune-Hyoun Kim, Byung-Su Park, Kwang-Seung Park.
Application Number | 20130121016 13/809864 |
Document ID | / |
Family ID | 45613126 |
Filed Date | 2013-05-16 |
United States Patent
Application |
20130121016 |
Kind Code |
A1 |
Kim; Byung-Mook ; et
al. |
May 16, 2013 |
OPTICAL FILM HAVING IMPROVED OPTICAL PERFORMANCE, AND BACKLIGHT
UNIT COMPRISING THE SAME
Abstract
The present invention relates to an optical film having improved
optical performance and to a backlight unit comprising the same.
More particularly, the present invention relates to a microlens
array (MLA) sheet which comprises a base unit and a lens unit
formed on one side of the base unit, wherein the lens unit consists
of a plurality of conical lenses. Existing hemispherical microlens
array sheets have limitations in terms of improving luminance, and
therefore cannot replace prism sheets in high luminance products.
However, the microlens array sheet consisting of conical lenses of
the present invention can improve both luminance and viewing angle
characteristics.
Inventors: |
Kim; Byung-Mook; (Jung-gu,
KR) ; Park; Kwang-Seung; (Yuseong-gu, KR) ;
Park; Byung-Su; (Seo-gu, KR) ; Kim; Yune-Hyoun;
(Seo-gu, KR) ; Han; Sang-Choll; (Yuseong-gu,
KR) ; Kim; Jin-Hyun; (Yuseong-gu, KR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Kim; Byung-Mook
Park; Kwang-Seung
Park; Byung-Su
Kim; Yune-Hyoun
Han; Sang-Choll
Kim; Jin-Hyun |
Jung-gu
Yuseong-gu
Seo-gu
Seo-gu
Yuseong-gu
Yuseong-gu |
|
KR
KR
KR
KR
KR
KR |
|
|
Assignee: |
LG CHEM., LTD
Seoul
KR
|
Family ID: |
45613126 |
Appl. No.: |
13/809864 |
Filed: |
July 14, 2011 |
PCT Filed: |
July 14, 2011 |
PCT NO: |
PCT/KR11/05183 |
371 Date: |
February 1, 2013 |
Current U.S.
Class: |
362/600 ;
359/709; 362/97.1 |
Current CPC
Class: |
G02F 1/133606 20130101;
G02B 3/0037 20130101 |
Class at
Publication: |
362/600 ;
359/709; 362/97.1 |
International
Class: |
G02B 3/00 20060101
G02B003/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 15, 2010 |
KR |
10-2010-0068531 |
Nov 26, 2010 |
KR |
10-2010-0118754 |
Claims
1. A microlens array (MLA) sheet comprising a base and a lens part
disposed on a surface of the base, wherein the lens part comprises
conic lenses that are determined by Equation 1 below, y = x 2 / r 1
+ 1 - ( 1 + k ) ( 1 / r ) 2 x 2 Equation 1 ##EQU00003## where k is
a conic constant, and r is a radius of curvature at a vertex of the
conic lens.
2. The microlens array sheet of claim 1, wherein k is a conic
constant that ranges from -3 to -1.
3. The microlens array sheet of claim 1, wherein k is a conic
constant that ranges from -2.7 to -14.7.
4. The microlens array sheet of claim 1, wherein k is a conic
constant that ranges from -2.65 to -1.75.
5. The microlens array sheet of claim 1, wherein the conic lens
comprises a hyperbola or a parabola in a central vertical
cross-section thereof.
6. The microlens array sheet of claim 1, wherein the conic lenses
have a pitch ranging from 10 m to 500 m.
7. The microlens array sheet of claim 1, wherein a bottom sur face
of the conic lens has a diameter ranging from 90% to 116% of a
pitch of the conic lenses.
8. The microlens array sheet of claim 1, wherein a bottom surface
of the conic lens has a diameter ranging from 92% to 116% of a
pitch of the conic lenses.
9. The microlens array sheet of claim 1, wherein a bottom surface
of the conic lens has a diameter ranging from 98% to 116% of a
pitch of the conic lenses.
10. The microlens array sheet of claim 1, wherein the radius of
curvature at the vertex of the conic lens ranges from 0.2% to 26%
of a pitch of the conic lens.
11. The microlens array sheet of claim 1, wherein the radius of
curvature at the vertex of the conic lens ranges from 0.2% to 24%
of a pitch of the conic lens.
12. The microlens array sheet of claim 1, wherein the radius of
curvature at the vertex of the conic lens ranges from 0.2% to 22%
of a pitch of the conic lens.
13. The microlens array sheet of claim 1, wherein the conic lenses
are uniformly arrayed.
14. A microlens array (MLA) sheet comprising a base and a lens part
disposed on a surface of the base, wherein the lens part comprises
conic lenses that comprises a hyperbola or a parabola in a central
vertical cross-section thereof.
15. The microlens array sheet of claim 14, wherein the conic lenses
are uniformly arrayed.
16. A backlight unit comprising: light sources; and the microlens
array sheet of claim 1.
17. The backlight unit of claim 16, wherein the microlens array
sheet is provided in duplicate, and the backlight unit comprises
the two microlens array sheets.
18. The backlight unit of claim 16, wherein the backlight unit
comprises one of a direct-type backlight unit and an edge-type
backlight unit.
Description
TECHNICAL FIELD
[0001] The present invention relates to an optical sheet and a
backlight unit including the optical sheet, and more particularly,
to a microlens array sheet having an enhanced optical performance
and a backlight unit including an optical film having the microlens
array sheet.
BACKGROUND ART
[0002] Liquid crystal display devices are electronic devices, which
use variations in the transmissivity of liquid crystals according
to voltage applied thereto to convert electrical information
generated from various devices into visual information.
[0003] Liquid crystal display devices, which are small,
lightweight, and economical in terms of power consumption, have
largely replaced cathode ray tubes, and are in use in various data
processing devices.
[0004] In such a liquid crystal display device, voltages are
applied to a liquid crystal material to change specific molecular
arrangements thereof. According to changes of the molecular
arrangements, optical characteristics of the liquid crystal
material also change, thereby displaying an image. The optical
characteristics of the liquid crystal material include
birefringence, optical rotatory power, dichroism, and light
scattering.
[0005] As liquid crystal displays do not themselves produce light,
they require a source of illumination in order to produce a visible
image. To this end, backlight units may be used therefor.
[0006] Backlight units may be classified into edge-type backlight
units and direct-type backlight units according to a position of a
light emitting device therein. Edge-type backlight units include a
light emitting device at a side of a light guide panel that guides
light emitted from the lamp. Edge-type backlight units are used in
small liquid crystal display devices such as the monitors of
desktop and notebook computers, and provide even lighting and good
durability. Moreover, the edge-type backlight units make possible
the slimming of a device including the edge-type backlight unit.
Meanwhile, the direct-type backlight units are used in 20-inch or
larger display devices. Such a direct-type backlight unit includes
lamps arrayed under a liquid crystal panel to directly illuminate
the liquid crystal panel.
[0007] Linear light sources such as a cold cathode fluorescent lamp
(CCFL) were previously widely used as light emitting devices in
backlight units, but recently, linear light sources have
increasingly been replaced with light emitting diodes (LEDs), which
are slim, lightweight, economical in terms of power consumption,
have excellent color reproducibility, and are environmentally
sound.
[0008] A backlight unit may include a combination of optical films
to diffuse or collect light emitted from a light source and improve
the brightness and unevenness of the lighting thereof.
[0009] Brightness and viewing angle are important factors in
evaluating image display devices such as liquid crystal display
devices, and are largely determined by the performance of an
optical sheet constituting a backlight unit. In recent years,
hemisphere-shaped microlens array sheets have been widely used, but
they have a limitation in improving brightness, and the brightness
must be sacrificed in order to improve a viewing angle thereof.
[0010] Today, active research and development is being carried out
into creating slim and lightweight backlight units. In particular,
microlens array sheets are required to have optical performances
such as high levels of brightness and wide viewing angles.
DISCLOSURE
Technical Problem
[0011] An aspect of the present invention provides a microlens
array (MLA) sheet including conic lenses to improve the brightness
and viewing angle thereof.
[0012] Another aspect of the present invention provides a backlight
unit including the microlens array (MLA) sheet to improve optical
performances thereof.
Technical Solution
[0013] According to an aspect of the present invention, there is
provided a microlens array (MLA) sheet including a base and a lens
part disposed on a surface of the base, wherein the lens part
includes conic lenses that are determined by Equation 1 below,
y = x 2 / r 1 + 1 - ( 1 + k ) ( 1 / r ) 2 x 2 Equation 1
##EQU00001##
where k is a conic constant that ranges from -3 to -1, and r is a
radius of curvature at a vertex of the conic lens.
[0014] The conic lens may include a hyperbola or a parabola in a
central vertical cross-section thereof.
[0015] The conic lenses may have a pitch ranging from 10 .mu.m to
500 .mu.m.
[0016] A bottom surface of the conic lens may have a diameter
ranging from 90% to 116% of a pitch of the conic lenses.
[0017] The radius of curvature at the vertex of the conic lens may
range from 0.2% to 26% of a pitch of the conic lens.
[0018] The conic lenses may be uniformly arrayed.
[0019] According to an aspect of the present invention, there is
provided a microlens array (MLA) sheet including a base and a lens
part disposed on a surface of the base, wherein the lens part
includes conic lenses that include a hyperbola or a parabola in a
central vertical cross-section thereof.
[0020] The conic lenses may be uniformly arrayed.
[0021] According to an aspect of the present invention, there is
provided a backlight unit including: light sources; and the
microlens array sheet of any one of claims 1 to 8.
[0022] The microlens array sheet may be provided in duplicate, and
the backlight unit may include the two microlens array sheets.
[0023] The backlight unit may include one of a direct-type
backlight unit and an edge-type backlight unit.
Advantageous Effects
[0024] Since hemisphere-shaped microlens array sheets in the
related art have a limitation in improving the brightness thereof,
the hemisphere-shaped microlens array sheets cannot replace a prism
sheet for a high brightness product. However, the microlens array
sheets including the conic lenses according to the embodiments of
the present invention have excellent brightness and viewing angle
performances.
DESCRIPTION OF DRAWINGS
[0025] FIG. 1 is a schematic view illustrating (a) a conic lens,
(b) hemisphere-shaped lens and (c) a cone-shaped lens constituting
a microlens array sheet, according to an embodiment of the present
invention.
[0026] FIG. 2(a) is a plan view and (b) is a cross-sectional view
illustrating a microlens array sheet according to an embodiment of
the present invention.
[0027] FIG. 3 is a view illustrating a backlight unit including
microlens array sheets (4, 4') having conic lenses according to an
embodiment of the present invention.
[0028] FIG. 4 is a graph illustrating brightness performances of
one, two, and three microlens array sheets according to an
embodiment of the present invention.
BEST MODE
[0029] Exemplary embodiments of the present invention will now be
described in detail with reference to the accompanying
drawings.
[0030] According to an embodiment of the present invention, an
optical sheet includes conic-shaped unit lenses arrayed in a
microlens array (MLA) on a light emitting surface. That is, a
microlens array (MLA) sheet includes a base and a lens part placed
on a surface of the base. The lens part includes conic lenses, each
of which includes a hyperbola or a parabola as the central vertical
cross-section thereof.
[0031] According to embodiments of the present invention, a conic
lens may be any symmetrical lens, provided that the symmetrical
lens includes a circular bottom surface and another surface
including a hyperbola or a parabola in the central vertical cross
section thereof. However, the conic lens is distinct from a
cone-shaped lens having a triangle as the central vertical
cross-section thereof, a hemisphere-shaped lens having a semicircle
as the central vertical cross-section thereof, and an
ellipse-shaped lens having an ellipse as the central vertical
cross-section thereof.
[0032] The shape of the conic lens may be determined by the
following equation, in which r denotes the radius of curvature at
the vertex of the conic lens, and k denotes the conic constant. The
shape of a curved surface constituting a lens may be expressed by a
function with the conic constant k and the radius of curvature r at
the vertex of the lens as variables. The conic constant k is a
factor for determining the shape of a lens. If k=0, a lens has a
circular shape. If k=-1, a lens has a parabola shape. If
-1<k<0, a lens has an ellipse shape. If k<-1, a lens has a
hyperbola shape.
y = x 2 / r 1 + 1 - ( 1 + k ) ( 1 / r ) 2 x 2 Equation 1
##EQU00002##
[0033] According to embodiments of the present invention, the conic
constant k of a conic lens may be in a range from -3 to -1,
preferably from -2.7 to -1.7, and more preferably, from -2.65 to
-1.75. FIG. 1(a) is a schematic view illustrating a conic lens
according to an embodiment of the present invention. FIGS. 1(b) and
1(c) are schematic views illustrating a hemisphere-shaped lens and
a cone-shaped lens, respectively, which are distinct from a conic
lens of the present invention. If the conic constant k is smaller
than -3, a brightness performance of a lens may be degraded. If the
conic constant k is greater than -1, an optical hiding performance
as well as the brightness performance may be degraded.
[0034] Conic lenses according to the embodiment maybe arrayed with
a predetermined pitch P on a surface of a microlens array sheet.
The pitch P may be in a range preferably from 10 .mu.m to 500
.mu.m, and more preferably from 30 .mu.m to 70 .mu.m. If a pitch of
lenses is smaller than 10 .mu.m, the lenses may overlap each other
to thereby degrade light-collecting efficiency, a mold fabrication
may be difficult, and the lenses maybe susceptible to scratches. If
a pitch of lenses is greater than 500 .mu.m, gaps may be formed
between the lenses to cause a loss of brightness, and the
fabrication cost of a mold may increase. The above-described ranges
of the pitch P according to the embodiment are determined to
address various issues during a lens fabrication and a defective
appearance such as a moire after the lens fabrication.
[0035] In addition, the shape of the conic lens may be determined
by a diameter D of the bottom surface of the lens and a height H
thereof. The diameter D may preferably be in a range from 90% to
116% of the pitch P, and more preferably from 92% to 116% of the
pitch P, and most preferably from 98% to 116% of the pitch P. If
the diameter D is smaller than 90% of the pitch P or greater than
116% thereof, the workability and yield of a film fabrication may
decrease, and the brightness of the lenses may be degraded. Thus,
when the lenses are disposed within the above-described ranges of
the diameter D, a desired light-collecting efficiency can be
attained.
[0036] The conic lenses may have various diameters within the
above-described ranges of the diameter D, but the conic lenses may
have the same diameter to facilitate lens fabrication and achieve
uniform light emittance.
[0037] The conic lenses may have various heights within the
above-described ranges of the height H, but the conic lenses may
have the same height to facilitate lens fabrication and achieve
uniform light emittance.
[0038] That is, the conic lenses may have various pitches within
the above-described ranges of the pitch P and the above-described
ranges of the diameter D, but the conic lenses may all have the
same pitch. FIG. 2(a) is a plan view illustrating a microlens array
sheet according to an embodiment of the present invention, and FIG.
2(b) is a cross-sectional view illustrating the microlens array
sheet of FIG. 2(a), in which lenses are uniformly arrayed. However,
arrangements of conic lenses according to the present invention are
not limited to FIGS. 2(a) and 2(b). For example, conic lenses
according to the present invention may be arrayed without gaps. In
this case, the density of the amount of conic lenses may increase,
and light-collecting efficiency using inclination surfaces of the
lenses can be ensured.
[0039] The radius of curvature r at the vertex of the conic lens
may preferably be in a range from 0.2% to 26% of the pitch P, more
preferably from 0.2% to 24% of the pitch P, and most preferably
from 0.2% to 22% of the pitch P. If the radius of curvature r is
smaller than 0.2% of the pitch P, a defect may occur at the vertex
of the lens during lens fabrication, the lens may be susceptible to
a scratch, air bubbles may be formed in the lens, and a fabrication
time may be increased. If the radius of curvature r is greater than
26% of the pitch P, the light-collecting efficiency, the optical
hiding performance, and the brightness performance may be
degraded.
[0040] A method of fabricating the microlens array sheet according
to the embodiment of the present invention may be any well-known
method in the art. For example, the conic lens according to the
embodiment of the present invention may be fabricated by placing a
lens-shaped intaglio mold on a base, injecting a thermosetting
resin into the mold, and curing the thermosetting resin.
Furthermore, an asymmetric bead arrangement method, a laser mask
etching method, a direct tooling method, or a photolithography
method may be used to fabricate the microlens array sheet.
[0041] The thermosetting resin used for fabricating the microlens
array sheet according to the embodiment of the present invention
may be one of urethane acrylate, epoxy acrylate, ester acrylate, a
radical-generating monomer, and a combination thereof. Molds having
various intaglios may be used to fabricate lenses having various
shapes, heights, and pitches. Aside from the above-described
methods, other well-known methods may be used to fabricate the
microlens array sheet of the present invention.
[0042] According to an embodiment of the present invention, the
microlens array sheet may be provided in plural, and a backlight
unit may include at least one of the microlens array sheets.
[0043] Backlight units having the microlens array sheets include a
direct-type backlight unit and an edge-type backlight unit.
[0044] That is, according to the embodiment of the present
invention, a backlight unit includes light sources and at least one
of the microlens array sheets over the light sources. Preferably,
two or more of the microlens array sheets may be disposed over the
light sources. More preferably, two of the microlens array sheets
may be disposed over the light sources.
[0045] FIG. 3 is a schematic view illustrating a direct-type
backlight unit according to an embodiment of the present invention.
Referring to FIG. 3, the direct-type backlight unit may include: a
reflective plate (1) reflecting otherwise wasted light back to a
light emitting surface; linear light sources (2) spaced apart from
one another at a constant distance; a diffuser plate or sheet (3)
transforming the linear light sources to a surface light source and
supporting optical films; and one or more microlens array sheets
(4) and (4') including conic lenses and disposed over the diffuser
plate or sheet.
[0046] The backlight unit may further include a diffuser film at
the upper or lower side of the microlens array sheets, or include a
light collecting film and a diffuser film, such as a prism film and
a lenticular lens film, at the upper or lower side of the microlens
array sheets.
[0047] The backlight unit can have wide viewing angle and high
brightness performance.
[0048] Hereinafter, exemplary embodiments of the present invention
will now be described in more detail, but the present invention is
not limited thereto.
MODE FOR INVENTION
Embodiment
[0049] 1. Fabrication of Microlens Array Sheet
Embodiment 1: Microlens Array Sheet Including Conic Lenses
[0050] A microlens array sheet was fabricated using a laser mask
method. The diameter D was 55 .mu.m. The radius of curvature r at
the vertex of a conic lens was 5.5 .mu.m. The conic constant k was
-2.15. The pitch P was 50 .mu.m.
COMPARATIVE EXAMPLE 1
Microlens Array Sheet Including Cone-Shaped Lenses
[0051] A microlens array sheet was fabricated in the same manner as
that of embodiment 1, except that cone-shaped lenses having a
vertical angle of 90.degree. were arrayed thereon and the diameter
D was 50 .mu.m and the pitch P was 50 .mu.m.
COMPARATIVE EXAMPLE 2
Microlens Array Sheet Including Hemisphere-Shaped Lenses
[0052] A microlens array sheet was fabricated in the same manner as
that of embodiment 1, except that hemisphere-shaped lenses having a
conic constant of 0 were arrayed and the diameter D was 50 .mu.m
and the pitch P was 50 .mu.m and the radius of curvature r at the
vertex of the hemisphere-shaped lens was 25 .mu.m.
EMBODIMENTS 2 TO 9, AND COMPARATIVE EXAMPLES 3 TO 20
[0053] Microlens array sheets were fabricated in the same manner as
that of the embodiment 1 by varying the pitch P, the diameter D,
the radius of curvature r, and the conic constant k, as shown in
the table below.
[0054] 2. Comparison of Brightness Performances According to Lens
Shapes
[0055] Each of the microlens array sheets fabricated as described
above was provided in duplicate to perform an optical simulation.
Here, light emitting diodes of a 22-inch edge-type backlight unit
were used for input values, and a receiver was disposed over the
two same microlens array sheets to compare viewing angle data
according to brightness. Simulation results are shown in the table
1.
[0056] In the table 1, the brightness of light incident to an
optical film is set to 100%, and a ratio of the maximum brightness
of light transmitted by the microlens array sheet to the brightness
of the light incident to the optical film is expressed in %.
TABLE-US-00001 TABLE 1 RADIUS OF CONIC DIAMETER PITCH CURVATURE (r)
CONSTANT (k) (D) (P) BRIGHTNESS UNIT .mu.m .mu.m .mu.m .mu.m %
EMBODIMENT 1 5.5 -2.15 55 50 100 COMPARATIVE EX 1 0.01 -2 50 50 85
COMPARATIVE EX 2 25 0 50 50 84 COMPARATIVE EX 3 12 -2.15 55 50 85
COMPARATIVE EX 4 5.5 -4 55 50 83 COMPARATIVE EX 5 5.5 -2.15 30 50
72 COMPARATIVE EX 6 5.5 -2.15 80 50 85 COMPARATIVE EX 7 5.5 -2.15
55 25 69 COMPARATIVE EX 8 5.5 -2.15 55 75 80 COMPARATIVE EX 9 5.5
-0.9 55 30 72 EMBODIMENT 2 1.3 -2.1 10 10 93 EMBODIMENT 3 5.2 -2 41
40 92 EMBODIMENT 4 9 -2 72 70 94 EMBODIMENT 5 63 -2 515 500 94
EMBODIMENT 6 5.5 -1 55 50 90 EMBODIMENT 7 5.5 -3 55 50 93
EMBODIMENT 8 5.5 -1.5 55 50 92 EMBODIMENT 9 5.5 -2.5 55 50 95
COMPARATIVE EX 5.5 -2.15 30 50 76 10 COMPARATIVE EX 50 -2.15 55 50
67 11 COMPARATIVE EX 5.5 -5 55 50 66 12 COMPARATIVE EX 1.3 -2.1 30
10 66 13 COMPARATIVE EX 10 -2.1 10 10 50 14 COMPARATIVE EX 1.3 -1.1
10 10 62 15 COMPARATIVE EX 63 -2 220 500 66 16 COMPARATIVE EX 200
-2 515 500 59 17 COMPARATIVE EX 63 -4 515 500 63 18
[0057] As shown in the table 1, the microlens array sheets
including the conic lenses according to the embodiments are
improved in brightness performance with respect to viewing angle in
comparison to the microlens array sheets including the
hemisphere-shaped lenses and the cone-shaped lenses in comparative
examples 1 and 2.
[0058] Furthermore, as shown in the table 1, the lenses disposed in
the above-described ranges of the pitch P and the conic constant k
according to the embodiment are improved in brightness performance
in comparison to the lenses disposed outside of the above-described
ranges of the pitch P and the conic constant k.
[0059] In particular, the microlens array sheets in the embodiments
significantly improved in brightness performance in comparison to
the microlens array sheets including ellipse lenses (k=0.9) in
comparative example 9.
[0060] 3. Comparison of Brightness Performances According to Sheet
Arrangement of the Present Invention
[0061] To compare brightness performances according to an
arrangement of microlens array sheets of the present invention, the
brightness performances of one microlens array sheet, two microlens
array sheets, and three microlens array sheets were compared to one
another.
[0062] To this end, an optical simulation was performed. Here,
light emitting diodes of a 22-inch edge-type backlight unit were
used for input values, and a receiver was disposed over two
microlens array sheets to compare viewing angle data according to
brightness. Simulation results are illustrated in FIG. 4.
[0063] Referring to FIG. 4, the brightness performance of the two
microlens array sheet is better than that of the one or three
microlens array sheets.
[0064] Therefore, when the lens shapes of a microlens array sheet
satisfy the ranges of the pitch P, the diameter D, the radius of
curvature r, and the conic constant k according to the embodiment,
and especially, when two microlens array sheets are used, the
brightness performance thereof can be significantly enhanced.
SEQUENCE LIST TEXT
[0065] P: pitch of the conic lens [0066] D: diameter of bottom
surface of the conic lens [0067] H: height of the conic lens [0068]
1: reflective plate [0069] 2: light sources [0070] 3: diffuser
plate [0071] 4, 4': microlens array sheet of present invention
* * * * *